Whoah, this should have been changed a long time ago. For one thing, Richard

forgot to update the copyright date when he made modifications in 1999, but more
significantly, this COPYRIGHT notice hasn't been changed since Richard ceded
control of nmh development and it became an open-source project.

Changed the COPYRIGHT notice to a BSD License, with a couple of minor wording
tweaks.  Copyright is assigned to "the authors of nmh", which is anyone who
writes code, whether they have CVS accounts or not.